The primary goals of the Cellular Biochemistry Group are to determine the composition and functional features of the supramolecular complex of proteins that calcifies, and how cells regulate this process. Towards these aims, cell cultures that support and form mineralized tissues are established for biochemical analysis, and for studies at the genomic level in collaboration with Drs. Marian F. Young and Larry W. Fisher. It is now recognized that bone formation is carried out by cells in the osteoblastic lineage which go through a series of maturational stages. It is hypothesized that these stages of maturation differ from each other in the set of extracellular matrix proteins that they produce, and in fact that cell-matrix interactions in part mediate the passage of the cells from one stage to another. In addition, other metabolic properties, such as cell surface markers, receptors, etc., likely change as the cells progress. Starting with cultures of uncommitted marrow stromal fibroblasts, which contain osteogenic precursors, at least in part, and cultures of more committed osteoblastic cells, the biochemical profile of the cells at different stages of maturation are being characterized through immunohistochemical surveys, identification of developmentally regulated proteins through molecular biological techniques, development of antibodies against newly identified proteins, identification of factors that regulate proliferation and differentiation, and studying characterizing cell-matrix interactions.